Releasing slips for oil well tool

ABSTRACT

Releasing slips for use with a downhole tool, a tool for deploying downhole in a well utilizing the releasing slips and a well in which a downhole tool is deployed utilizing the releasing slips of the invention is described herein. The tool has a plurality of slips for selective engagement with a wall of a wellbore. The slips include releasing slips and biting slips. The releasing slips have a low friction surface, e.g., a substantially smooth surface for engaging the wall of the wellbore. The smooth wall engaging face of the releasing slips facilitate easy release of the slips, thereby facilitating easy removal of the downhole tool. The slips may include a plurality of hardened members that protrude from the wall engaging face of the releasing slips to reduce wear on the face of the releasing slip.

FIELD OF THE INVENTION

The invention relates to an improved releasing slip for use with a hold down tool/bridge plug/packer for lowering into a wellbore. In particular, the releasing slip of the invention has a low friction face to facilitate ease of release.

BACKGROUND OF THE INVENTION

A production packer is a standard component of completion hardware in oil and gas wells. Production packers are used to provide a seal between the outside of production tubing and the inside of a casing, liner, or wellbore wall. When recovering oil and gas from a well, in many geological formations it is necessary to isolate the zone containing the oil and gas producing formation from the remainder of the underground structure so as to prevent contamination of the oil and gas producing zone from salt water or other undesirable contaminants.

Packers may be lowered into the well and expanded to isolate the oil and gas producing zone. Packers may be placed above and below the producing zone, or, if the producing zone is near the bottom of the well, a single packer may be placed above the producing zone. Packers are typically provided with slips for providing gripping engagement with the wall of a wellbore. Once a packer is set, the packer may experience forces that could displace the packer in the casing. One example of such a force is pressure from the formation.

In some circumstances, it may be desirable to utilize a hold down tool or bridge plug in the well to assist in keeping a packer in position. A hold down tool/bridge plug typically includes a plurality of slips that may be selectively forced into tight engagement with a wall of the well bore.

One difficulty associated with the use of conventional slips or gripping members is that the slips that are engaged with the wellbore can be extremely difficult to release when it is desired to release the tool.

An innovative oil well hold down tool is taught in U.S. Pat. No. 3,356,141 to Albert K. Kline (the '141 patent). The system taught in the '141 patent provided for one or more slips to be released prior to release of all the loaded slips, depending on the circumference of the tool used. The early releasing slips have become known as “releasing slips”. When the releasing slip or slips are released, normally by pulling up against them or their mounting device, the tool as a whole is then free to move laterally in the well slightly. The lateral movement of the tool is enough to lessen or remove entirely the bite of the remaining slips. The tool can then be moved up the well, or relatched and then moved further down the well and reset, or removed entirely.

There are numerous uses of the releasing slip principle taught by the '141 patent. Applicant's company manufactures several tools utilizing the teachings of the '141 patent. For example, one tool addressed improvements to the invention of the '141 patent related to the releasing slips. The device was used to assist in the release of hold down tools that have mechanically, as opposed to hydraulically, loaded slips above the pack-off portion of the tool.

One drawback of hold down tools utilizing prior art designs is that, when engaged, the slips bite into the casing wall while the hold down tool is performing its functions. Therefore, during release, even the releasing slips provide resistance, which causes problems including that the biting surfaces of the releasing slips become worn fairly quickly, requiring their replacement. An additional difficulty is that during higher pressure operations, the releasing slips can provide sufficient resistance that release becomes difficult and may also cause other problems. These problems may include overstressing the pulling unit topside, parting of the tubing that is used to transfer the tension from the pulling unit to the tool, rupture or permanent deformation of the mounting device for the slips, and ultimately, an inability to remove the tool at all.

SUMMARY OF THE INVENTION

This present invention replaces the releasing slips with a part or parts that have no biting effect on the casing. In one embodiment, the surface of the releasing slip of the present invention is entirely smooth. When pulled upwards, the releasing slips of the present invention move up much more easily, allowing the tool to move laterally, thereby partially unloading the remaining slips, and thus allowing the remaining slips to more easily release. The releasing slips in this case are, in practice, used as a wedge, which allow the remaining slips to function normally. The releasing slips of the invention are not required to provide biting capability for the hold down tool to perform its function. The releasing slips of the invention allow the tool to release much more easily, especially in severe applications.

A second embodiment of the present invention utilizes one or more hardened carbide pieces or other suitable material on the contacting face of the releasing slip of the invention. The smooth surface of the hardened piece or pieces are preferably configured such that the piece or pieces lay flat against a wall, thereby providing greatly reduced resistance to release. The carbide pieces are harder than any standard grade of casing, which greatly reduces wear on the part.

In the case of larger diameter tools, more than one releasing slip may be used in the circumferential arrangement of the upper slips. Preferably, the releasing slips cover somewhat less than half the circumference of the tool so that the tool can move laterally in the wellbore when the releasing slips are released or disengaged from the wellbore wall. The biting slips preferably also encompass less than half the circumference. As an example, a hold down tool of the present invention may use two releasing slips and four biting slips, although other numbers of slips and ratios of releasing slips to biting slips may be functional. In a preferred embodiment, the releasing slips are wider than the biting slips and the biting slips encompass less than 180 degrees of tool circumference.

There are several advantages of the present invention. Most importantly, a tool utilizing the inventive slips significantly reduces the problems described above with respect to removal of the tool. The monetary benefit associated with the tool includes the relatively smaller benefits associated with improved service life of the releasing slips and also the substantially larger benefits associated with avoiding an inability to release the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned elevation view of a packer being placed in a hole, attached to a hold down tool, in which the invention is embodied.

FIG. 2 is the structure of FIG. 1 attached at a desired position within a well bore.

FIG. 3 is an isometric view of a slip housing base of the hold down tool of FIG. 1.

FIG. 4 is an isometric view of the slip housing of FIG. 3 shown with slips installed therein.

FIG. 5 is an isometric view of a biting slip for installation into the slip housing of FIG. 4,

FIG. 6 is an isometric view of a releasing slip for installation into the slip housing of FIG. 4.

FIG. 7 is an isometric view of a releasing slip of FIG. 4 with carbide pieces on a wall engaging face of the releasing slip.

FIG. 8 is a partial cut-away view of a retrievable bridge plug in which the invention is embodied.

FIG. 9 is a partial cut-away view of a packer in which the invention is embodied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first primarily to FIGS. 1 and 2, shown is well bore 10 having a wall 12. A packer 14 is shown lowered into well bore 10. Packer 14 includes an expansible element such as packer slips 15 for selectively engaging wall 12. A hold down tool 16 is connected to packer 14. Hold down tool 16 includes a cone assembly 18. Cone assembly 18 has an upwardly facing cone 20 and an outer casing 22. Outer casing 22 defines a j-slot 24 having a long vertical section 26 and a short horizontal section 28. Cone assembly 18 further defines an internal abutment 30.

A coupling member 32 is attached to an upper end of hold down tool 16. A tubing string 34 is connected to coupling member 32 for supporting hold down tool 16 and packer 14 within well bore 10.

A spring 36 is located above hold down tool 16. Spring 36 has an upper end in abutment with coupling member 32. A cylindrical mandrel 38 extends downwardly inside cone assembly 18. Mandrel 38 defines a protuberance 40 and has a lower end 42. Mandrel 38 further has a pin 44 protruding from an outer surface. Pin 44 is provided for extending into j-slot 24.

Mandrel 38 and cone assembly 18 are releasably connected together via pin 44 and j-slot 24. When pin 44 is positioned in long vertical section 26 of j-slot 24, mandrel 38 may be moved downwardly (as shown in FIG. 2) until lower end 42 of mandrel 38 seats on internal abutment 30 of cone assembly 18.

Slip housing 46 is located above cone assembly 18. Slip housing 46 is made up of a slip housing cover 48 (FIGS. 1, 2, 4) and a slip housing base 50 (FIGS. 3, 4). Slip housing base 50 is slidably mounted on mandrel 38. Slip housing cover 48 and slip housing base 50 define an annular space therebetween. Slip housing base 50 has an upper end in engagement with a lower end of spring 36. Spring 36 urges slip housing base 50 against protuberance 40 on mandrel 38. Slip housing base 50 has a lower end defining a flange portion 52. Flange portion 52 defines a plurality of downwardly facing openings 54 (FIG. 3).

A plurality of slips 56 are carried within slip housing 46 and are sized to be received within openings 54 of slip housing base 50. Slips 56 each have an extension 58 (FIGS. 4-7) on an upper end for locating in the annular space between the slip housing cover 48 and the slip housing base 50. Slips also have a wall engaging face 60 (FIGS. 4-7). Slips 56 further define a slip neck 61 (FIGS. 5-7). Slips 56 are loosely received within openings 54 of slip housing base 50 wherein flange portions 52 of slip housing base 50 that are located between openings 54 provide supportive engagement with slip necks 61.

Slips 56 are comprised of biting slips 62 (FIGS. 4, 5) and releasing slips 66 (FIGS. 4, 6, 7). Faces 60 of biting slips 62 have a plurality of wickers or teeth 64 to facilitate gripping engagement with wall 12 of bore 10. Faces 60 of releasing slips 66 have smooth surface 68 to facilitate ease of release. In an alternative embodiment, smooth surface 68 of releasing slip 66 may be impregnated with one or more hardened carbide pieces 70 to reduce wear on face 60 of releasing slips 66.

Slip housing base 50 functions to selectively urge slips 56 downwardly when mandrel 38 is moved downwardly. Slips 56 are oriented vertically and are positioned circumferentially above upwardly facing cone 20 of hold down tool 16. Therefore, when slips 56 are moved downwardly with mandrel 38, slips 56 engage the upwardly facing cone 20. Upwardly facing cone 20 then forces engagement faces 60 proximate the lower ends of slips 56 outwardly into engagement with wall 12 of well bore 10.

When it is desired to release the slips 56, mandrel 38 is moved upwards. The force of the mandrel moving upward is first transmitted through slip housing base 50. Flange portion 52 of slip housing base 50 lifts slips 56 upwards. Slip necks 61 may be of different lengths, so that flange portion 52 does not engage slips simultaneously.

Referring now to FIG. 8, a bridge plug 100 is shown utilizing the slips of the invention. Bridge plug 100 includes a tubular housing 102. Tubular housing 102 is made up of lower mandrel 104, connecting rod 106 that is threadably received on an upper rod of lower mandrel 104, and an upper mandrel 108 that is threadably received on an upper end of connecting rod 106. A pulling head cap 110 is threadably received on an upper end of upper mandrel 108.

A control body 112 surrounds lower mandrel 104. A plurality of drag blocks 114 are supported by control body 112. Drag blocks 114 are biased outwardly by drag block springs 116.

A lower cone member 118 surrounds lower mandrel 104. Lower cone member 118 has a cone section 120 and a lower cylindrical section 122. A plurality of lower slips 124 surround lower cylindrical section 122 of lower cone member 118. Plurality of lower slips 124 are located below cone section 120 of lower cone member 118.

An element retainer 126 is threadably received on an upper end of lower cone member 118. Packing and seal sleeve 128 and attached packing element 130 are adjacent to connecting rod 106 in an abutment with element retainer 126. An upper cone member 132 is threadably received on an upper end of packing and seal sleeve 128.

A slip sleeve 134 is provided above upper cone member 132. A plurality of upper slips 136 surrounds slip sleeve 134. Upper slips 136 are made up of releasing slips 138 and biting slips 140. A thrust spring 142 is provided having a lower end in engagement with slip sleeve 134. A spring ring 144 is affixed to upper mandrel 108. Spring ring 144 is in engagement with an upper end of thrust spring 142.

In practice, when packing element 130 engages a wall of a wellbore, packing element 130 moves upwardly with regard to tubular housing 102 with attached upper cone member 132. Upper cone member 132 contacts upper slips 136 and forces slips 136 into engagement with a wall of the wellbore.

Referring now to FIG. 9, shown is a packer 200 utilizing the releasing slips of the invention. Packer 200 includes a mandrel 202. A top sub 204 is threadably attached to an upper end of mandrel 202. A control body 206 surrounds mandrel 202. A plurality of drag blocks 208 are supported by control body 206. Drag blocks 208 are biased outwardly by drag block springs 210.

A lower slip sleeve 212 is threadably attached to an upper end of control body 206. A lower cone member 214 surrounds lower slip sleeve 212. A plurality of lower slips 216 surround lower slip sleeve 212. The plurality of lower slips 216 are located below lower cone member 214.

An element retainer 218 is threadably received on an upper end of lower cone member 214. A packing and seal sleeve 220 as well as a packing element 222 are in threaded communication with element retainer 218.

An upper cone member 224 is threadably received on an upper end of packing and seal sleeve 220. An upper slip support 226 is located above upper cone member 224. A plurality of upper slips 228 surround upper slip support 226. Upper slips 228 are made up of releasing slips 230 and biting slips 232. A slip spring 234 is provided for biasing each of upper slips 228 outwardly. An upper slip housing assembly 236 is located above upper slips 228.

In practice, when packing element 222 engages a wall of the wellbore, packing element 222 moves upwardly with regard to mandrel 202. Attached upper cone member 224 moves upwards as well. Upper cone member 224 contacts upper slips 228 and forces slips 228 into engagement with a wall of the wellbore.

When pulled against for release, as described above, releasing slips 66 (FIGS. 4, 6, 7), 138 (FIG. 8), 230 (FIG. 9) are easily lifted and disengaged from wall 12 since releasing slips 66, 138, 230 have a low friction wall engaging face, as can best be seen in FIGS. 6 and 7. Once releasing slips 66, 138, 230 are lifted, tool 16, 100, 200 is able to move laterally, thereby partially unloading the remaining biting slips 62 (FIGS. 4, 5), 140 (FIG, 8), 232 (FIG. 9), which allows biting slips 62, 140, 232 to more easily release. Therefore, releasing slips 66, 138, 230 function as a wedge to force biting slips 62, 140, 232 to securely engage wall 12. Releasing slips 66, 138, 230 are not required to provide biting capability for tool 16, 100, 200 to perform its function. Releasing slips 66, 138, 230 of the invention allow tool 16 (FIGS. 1, 2), 100 (FIG. 8), 200 (FIG. 9) to release much more easily, especially in severe applications.

In one embodiment, hardened pieces 70 (FIG. 7), such as hardened carbide disks or pieces of other suitable material protrude from contacting face 60 of releasing slip 66, or from a contact face of releasing slips 138, 230. Smooth surface 68 of a hardened piece 70 or pieces 70 are preferably configured such that the piece or pieces 70 lay flat against wall 12, thereby providing greatly reduced resistance to release. The carbide pieces 70 are harder than any standard grade of casing, which greatly reduces wear on releasing slip or slips 66, 138, 230.

In the case of larger diameter tools 16, 100, 200, more than one releasing slip 66, 138, 230 may be used in the circumferential arrangement of the slips 56. Preferably, releasing slips 66, 138, 230 cover somewhat less than half the circumference of tool 16, 100, 200, so that tool 16, 100, 200 can move laterally in wellbore 10 when releasing slips 66, 138, 230 are released or disengaged from wall 12. Consequently, biting slips 62, 140, 232 preferably encompass more than half the circumference of tool 16, 100, 200.

Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims. 

1. A well comprising: a wellbore having a wall; a tool adapted for lowering into said wellbore, said tool having a plurality of slips for selective engagement with said wall; wherein said slips include releasing and biting slips; and wherein said releasing slips have a low friction wall engaging surface for engaging said wall.
 2. The well according to claim 1 wherein: said low friction wall engaging surface is substantially smooth.
 3. The well according to claim 1 wherein: said low friction wall engaging surface is comprised of a plurality of hardened members for engaging said wall.
 4. The well according to claim 1 wherein: said tool is a hold down tool.
 5. The well according to claim 1 wherein: said tool is a packer.
 6. The well according to claim 1 wherein: said tool is a bridge plug.
 7. The well according to claim 1 wherein: said releasing slips are located over less than half of a circumference of said tool.
 8. The well according to claim 1 wherein: said slips comprise two releasing slips and four biting slips.
 9. The well according to claim 1 wherein: said releasing slips are wider than said biting slips.
 10. A tool for lowering into a wellbore, said tool comprising: a body; a cone member slidable in a longitudinal direction along a length of said tool body for selective engagement with said plurality of slips for forcing slips outwards; a plurality of slips affixed to said body; wherein said slips include releasing and biting slips; wherein said biting slips have a gripping surface; and wherein said releasing slips have a low friction wall engaging surface.
 11. The tool according to claim 10 wherein: said low friction wall engaging surface is substantially smooth.
 12. The tool according to claim 10 wherein: said low friction wall engaging surface comprises a plurality of hardened members for engaging said wall.
 13. The tool according to claim 10 wherein: said tool is a hold down tool.
 14. The tool according to claim 10 wherein: said tool is a packer.
 15. The tool according to claim 10 wherein: said tool is a bridge plug.
 16. The tool according to claim 10 wherein: said releasing slips are located over less than half of a circumference of said tool.
 17. The tool according to claim 10 wherein: said slips comprise two releasing slips and four biting slips.
 18. The tool according to claim 10 wherein: said releasing slips are wider than said biting slips.
 19. A releasing slip for use in a tool for lowering into a wellbore, said slip comprising: a body; an extension extending upwardly from said body; and a low friction wall engaging face on said body to facilitate easy release.
 20. The releasing slip according to claim 19 wherein: said low friction wall engaging face is substantially smooth.
 21. The releasing slip according to claim 19 wherein: said low friction well engaging face further comprises a hardened member protruding from said face for reducing wear of said low friction wall engaging face. 